Persist a redacted chained traceback in the private run output and expose
redacted last_error in tool and slash listings, including historical errors.
Keep the run_job concise error return unchanged for delivery classification.
Slim redo of liuhao1024's earliest #104545; adds forced redaction and keeps
formatting in a topical sibling. Local SDK/socket A/B verifies diagnosis
visibility plus healthy-script, clearing, and private-file controls.
Canonical tests queued under the campaign lock at commit time.
Co-authored-by: liuhao1024 <sunsky.lau@gmail.com>
Teknium